The present invention relates to crystalline forms of a pyrimidine nucleoside derivative which exhibit excellent anti-tumour activity; to a pharmaceutical composition (preferably an anti-tumour agent) containing said crystalline form as an active ingredient; to the use of said crystalline form in the preparation of said pharmaceutical composition; and to a method for prevention or treatment of disease (preferably tumour) which comprises administering to a warm blooded animal (preferably a human) in need of such prevention or treatment a pharmacologically effective amount of said crystalline form.
[Background of the Invention]
The pyrimidine nucleoside derivative of formula (I) (hereinafter referred to as Compound (I)) has been disclosed in Japanese Patent No. 2569251 and U.S. Pat. No. 5,691,319. As described therein, compound (I) exhibits excellent anti-tumour activity and is expected to become an agent for treatment or prevention of tumours. To make Compound (I) more practical for use as a medicament, better storage stability, ease of handling and the like is required.